1. Field of the Invention
This invention relates to a microscope with a dynamic vibration absorber.
2. Description of Related Art
In a microscope of high resolving power, slight vibration will cause a great disturbance. Accordingly, measures against the vibration have been taken. For example, an air table and a rubber foot are used therefor.
The air table attenuates vibration from the floor by utilizing an air spring or the like and serves as a table for mounting a microscope. Further, there is proposed an air table in which a sensor detects vibration of the table to drive and control actuators provided between the floor and the table so that the vibration can be cancelled.
The rubber foot is arranged on the bottom surface of a microscope to prevent the microscope from becoming unsteady and to attenuate vibration transmitted from a surface on which the microscope is located. In addition, the rubber foot can reduce rolling or pitching of the whole microscope.
Furthermore we know a dynamic vibration absorber (a dynamic damper) which is a kind of means for attenuating vibration.
The dynamic vibration absorber reduces vibration by means of a force due to vibration of a mass and is divided into a passive dynamic vibration absorber and an active dynamic vibration absorber. The passive dynamic vibration absorber comprises a mass, a spring element, and a damping element. A plurality of masses, springs and/or damping elements may be used in some kinds of apparatus. The active dynamic vibration absorber uses a vibration sensor to detect vibration and drives a mass by means of an actuator to reduce the vibration. The dynamic vibration absorber is applied to various technologies such as construction and automobile industries and is disclosed in, for example, Japanese Laid-Open Patent Publication Nos. Hei 3-250165 and Hei 8-21483.
In the passive dynamic vibration absorber, the mass is secured via the spring element and the damping element to a structure whose vibration should be reduced. When the structure vibrates so that the relative displacement between the mass and the structure varies, vibration energy is consumed by the damping element between the mass and the structure, thereby attenuating the vibration.
In the active dynamic vibration absorber, the mass is secured via the actuator to a structure whose vibration should be reduced. After the vibration sensor detects vibration of the structure, the actuator drives the mass according to the detected vibration so that the vibration of the structure can be cancelled by a force of the mass.
As described above, in a microscope of high resolving power, vibration is reduced by means of an air table, a rubber foot, a dynamic vibration absorber, or the like. However, in recent years, these measures against the vibration have become insufficient.
For example, microscopes having a resolving power of 1 nm or less, such as a tunneling microscope (see U.S. Pat. No. 4,823,044) and an atomic force microscope (see U.S. Pat. Nos. 5,260,824 and 5,672,816), have been put to practical use. Further, a scanning laser microscope provides an observation image which is very clear in comparison with that of a conventional microscope. These microscopes require very strict setting environments. For example, air vibration caused by voice, noise, an air conditioner or the like will cause a deterioration of the observation image.
Further, a motor driving mechanism is incorporated in a microscope for electrical driving and is also a source of vibration. That is, when the driving mechanism operates to move a sample stage, perform focusing, or change over filters, prisms or the like, mechanical vibration is generated from the driving mechanism.
Under the circumstances, the air table is used for the measures against the vibration. The air table is to insulate a structure on the table from floor vibration and is not effective in insulating the structure from a disturbance, such as air vibration caused by voice, noise, an air conditioner or the like, and mechanical vibration generated by an electrically driven microscope itself.
The rubber foot is to prevent a microscope from being unsteady when it is installed, and to reduce rolling or pitching of the entire microscope. It does not directly contribute to reducing the vibration that varies the relative positions of a sample and an observation optical system.
The dynamic vibration absorber is used for reducing air vibration caused by voice, noise, an air conditioner or the like, and mechanical vibration generated by an electrically driven microscope itself that are applied to a structure affecting an observation image of a sample, such as an objective lens and a sample stage. That is, the dynamic vibration absorber is suitable for reducing local vibration, but has the problems that its setting place is restricted and that the microscope becomes heavy because the mass is used.
It is explained why the setting place is restricted. In the microscope, the structures whose vibration should be reduced are the sample stage and the observation optical system. In many cases, the observation optical system is supported by a cantilever-type frame. Since the cantilever-type frame has a shape that is susceptible to vibration, it is desired to reduce the vibration. However, as the observation optical system exists, the setting place of the dynamic vibration absorber is restricted. Accordingly, in the conventional microscope system, the space for incorporation the dynamic vibration absorber has not been studied.
The reason why the microscope becomes heavy due to the use of the mass is as follows: Since the passive dynamic vibration absorber has no vibration sensor, it cannot cope with a change of the structure whose vibration should be reduced, especially when the equivalent mass (mass of a physical model of a structure) of the mass is smaller than that of the structure whose vibration should be reduced. Since the frame of a microscope is highly rigid and its equivalent mass is large, a heavy mass is required. Accordingly, the microscope becomes heavy (and a large setting space is also necessary). When the microscope becomes substantially heavy, it is necessary to redesign the frame or the like.
In an embodiment of the present invention, a microscope having an optical axis has a frame including a base arm, a column extending vertically from the base arm and an upper arm. Adynamic damper includes a fixed part coupled to the upper side of the upper arm, and a movable part supported for linear movement in the direction of the optical axis with respect to the fixed part. An optical system is coupled to the movable part, the optical system comprising a displaceable mass of the dynamic damper. Parallel light rays extend along part of the optical axis, with the dynamic damper surrounding the optical axis at the position of the parallel light rays.
The microscope may also include a sensor for detecting vibration of the fixed part, and outputting a vibration signal, an actuator for moving the movable part in a direction of the optical axis; and a controller for outputting a driving signal to move the actuator, the driving signal generated on the basis of the vibration signal so as to attenuate the vibration.
A damping member for attenuating the vibration of the movable part with respect to the fixed part may be disposed between the movable part and the fixed part. The microscope may be, for example, a laser scanning microscope or a confocal microscope. The optical system may be an ocular tube or an ocular tube, and an intermediate attachment.